1. Field of the Invention
The present invention relates to chitosan derivatives and a method for preparing the same, in which a chitosan is combined with a polypropylene glycol.
2. Description of the Related Art
Chitosan is a basic polysaccharide, with a molecular weight of about 800,000 to 1,000,000, which is composed of D-glucosamine residues and N-acetyl-D-glucosamine residues and has beta-(1,4)-linked 2-amido-2-deoxy-D-glucose units.
Chitosan is obtained from deacetylated chitin contained in the skins of crabs (from Japan, U.S.A.), Krill (from Poland), shrimps (from India).
Now, a description will be given in detail as to a process for extracting chitosan from the skin of crabs by way of example.
First, the skin of crabs, which contains chitin (25-30%), calcium carbonate (40-50%) and proteins (20-30%) as principal gradients, is treated with a diluted hydrochloric acid or a diluted sodium hydroxide to remove calcium carbonate and proteins, respectively.
The chitin thus obtained is then deacetylated with a concentrated sodium hydroxide to yield a chitosan. The chitosan may have a desired degree of deacetylation depending on the reaction conditions. For example, the chitosan commercially available as a coagulator has a degree of deacetylation in the range from about 70 to 80%.
The chitosan plays an important role in a living body. For example, the chitosan mechanically supports cells in the tissue of the body and becomes a principal component of the extracellular medium to form the outer skeleton.
Also, the chitosan is a promising natural resource for beauty articles and currently studied in regard to its availability in various applications such as foods and medicinal substances.
Recently, chitin or chitosan is growingly prevailing as the use has been made of the hydrolysis products of chitin or chitosan, including lower monosaccharides (e.g., D-glucosamine and N-acetyl D-glucosamine) or oligosaccharides (e.g., chitin oligosaccharide and chitosan oligosaccharide).
However, the studies of the chitosan have been chiefly concentrated on the applications including film former, thickener, antibiotic, etc. and there have been no report on the chitosan derivatives used for stabilizer and moisturizer in cosmetics.
Such a limitation in the use results from the fact that the chitosan is insoluble in almost solvents and thus difficult to be used as a solution and that the chitosan may be slightly soluble in a diluted acid of similar properties but is insoluble in water or alcohol. Another reason for such a limitation in the cosmetic use is that the chitosan is almost incompatible with various effective gradients of the cosmetics such as plant extracts, proteins and derivatives thereof.
To overcome these problems, an attempt has been made to combine a hydrophobic fatty acid with the amino group or hydroxyl group of the chitosan, in which case the resulting chitosan has a low solubility in water and is not useful as a material for cosmetics.
Alternatively, an aqueous chitosan containing 1 or 2 moles of ethylene oxide added to the chitosan in order to make the chitosan more soluble in water has an excessively high solubility in water and forms a complex with natural extracts used in the cosmetics, which results in a long-term deterioration of the efficacy and effect of the cosmetics. Furthermore, the ethylene oxide is a toxic gas at the ambient temperature and causes some difficulties in the preparation of the cosmetics.
It is, therefore, an object of the present invention to solve the problems and to provide chitosan derivatives represented by the formula I, in which a chitosan is combined with a polypropylene glycol in order to make the chitosan have a required solubility and be compatible with other compounds of cosmetics.
It is another object of the present invention to provide a method for preparing the chitosan derivatives represented by the formula I.
It is further another object of the present invention to provide skin/hair cosmetics containing as an effective gradient the chitosan derivatives represented by the formula I.
To achieve the above objects of the present invention, there is provided chitosan derivatives combined with polypropylene glycol and a method for preparing the same, characterized in that the polypropylene glycol is grafted on the amino group or hydroxyl group of a chitosan or a partially deacetylated chitosan by nucleophilic substitution.